GHSA-72w7-mf9g-733p nono-py has proxy-only network fallback bypass on older Linux kernels

• PyPI nono-py: >= 0.9.0, < 0.10.1 → fixed in 0.10.1

Summary On Linux kernels that do not support Landlock network rules, `nono_py.sandboxed_exec()` could run `CapabilitySet.proxy_only(proxy)` without supervising the seccomp-notify proxy-only fallback returned by the Rust core. In that configuration, a sandboxed child process could remove `HTTP_PROXY` / `HTTPS_PROXY` environment variables or use raw sockets and then open direct TCP connections that should have been denied by proxy-only policy. The issue affects proxy-only enforcement. It does not mean that all nono-py network blocking is ineffective. ECS validation showed `caps.block_network()` denied regular TCP and ECS metadata TCP on the tested Linux 6.1 host. Impact The intended `proxy_only()` security property is: • child processes may connect only to the local nono proxy port • the proxy enforces host allowlists and metadata/link-local denial • direct TCP to any other target is denied Before the fix, on kernels without Landlock `AccessNet`, the Python binding applied the sandbox and then executed the child, but did not install and supervise the proxy-only seccomp-notify fallback. A child could therefore bypass the proxy layer in that old-kernel path. The highest-impact scenario is a sandboxed workload with access to cloud metadata discovery inputs, where direct TCP to a metadata endpoint could retrieve task or instance credentials after proxy environment variables are removed. Affected Conditions The issue requires all of the following: • Linux runtime. • Kernel without Landlock network support, such as Linux 6.1. Landlock network rules require Landlock ABI v4 / Linux 6.7 or newer. • `nono_py.sandboxed_exec()` is used. • The capability set uses `caps.proxy_only(proxy)`. • The child process removes or ignores proxy environment variables, or uses raw sockets. macOS Seatbelt proxy-only enforcement is not affected by this Linux seccomp-notify fallback issue. Affected Versions Known affected builds include nono-py versions that expose and use `CapabilitySet.proxy_only()` through `sandboxed_exec()` before the supervised fallback fix in this working tree. Earlier versions that did not expose `CapabilitySet.proxy_only()` are not affected by this specific proxy-only enforcement bug, though they may have separate environment-inheritance risks if callers passed broad parent environment variables into sandboxed children. CVSS Score Rationale | Metric | Value | Rationale | |---|---|---| | Attack Vector (AV) | L — Local | Exploit is performed by a local process (unsetting env vars or opening raw sockets). Not remotely triggerable. | | Attack Complexity (AC) | H — High | All of the following must be true: Linux runtime; kernel < 6.7 (no Landlock ABI v4); `sandboxed_exec()` used; capability set calls `proxy_only()`; child actively bypasses proxy env vars or uses raw sockets. | | Privileges Required (PR) | L — Low | Attacker is already executing code inside the sandbox — some user-level privilege is required to get there. | | User Interaction (UI) | N — None | No action from a user or operator is needed once the sandboxed child is running. | | Scope (S) | C — Changed | The exploit crosses the sandbox security boundary, allowing the child to reach network resources outside the defined policy scope. | | Confidentiality (C) | H — High | Highest-impact path: direct TCP to cloud metadata endpoint (169.254.169.254) yields IAM / task credentials. | | Integrity (I) | L — Low | Attacker can make arbitrary outbound requests; no direct data modification from the bypass itself, but lateral credential use creates indirect risk. | | Availability (A) | N — None | No denial-of-service impact described or implied. | ---